Lung transplantation (LT) is recognized as a common treatment option in a variety of end-stage pulmonary diseases. Improvements in recipient selection, surgical techniques, and immunosuppressive regimens have increased the survival following LT. However, the long-term survival of the lung allograft is limited by the development of bronchiolitis obliterans syndrome (BOS). Analysis of 339 LT patients performed during the past 8 years in our center have shown that 40% develop BOS within 2 years, and this incidence increases with time. We have obtained evidence that the development of anti-HLA alloantibodies and the detection of in vivo CD4+ T cell priming against donor HLA class I and II antigens precede and correlate with the development of BOS. Further, we have shown that change in immunosuppression based on the early detection of anti-HLA alloantibodies substantially improves the clinical course of the patients. Further, we have shown a significant role for airway epithelial cell (AEC)-specific non-HLA antibodies, matrix metalloproteinases, regulatory CD4+ T cell subpopulations, and innate immunity in the immunopathogenesis of BOS. Specific goals of this project are: 1) To continue to define the subgroup of LT recipients developing anti-HLA antibodies after LT and to institute a new treatment regimen in order to delay or prevent the onset of BOS. Based on the detection of HLA antibodies before any detectable decline in the pulmonary function, we will divide LT recipients into three groups. One group will be treated with FK506, Cellsept, and tetracycline (a matrix metalloproteinase-inhibitor), a second group will be treated with FK506 and Cellsept, and a third group will be continued on their standard therapy (CSA, prednisone, and Imuran). We expect that the third group will be discontinued during the first year since a statistically significant difference would have been obtained by that time. 2) To define the biology and biochemistry of the newly identified AEC-specific antigens. We will determine the polymorphism and biochemistry of this antigenic system by internal labeling of AECs, immunoprecipitation analysis and protein micro sequencing. In particular, we will determine the association of HSP60 with epithelial specific antigenic peptides in eliciting AEC-specific antibodies in patients with BOS. 3) To identify and characterize the regulatory T cell subpopulations associated with the lack of development of BOS. Our preliminary results have shown one or more Th2 cell subpopulations with either the CD4+CD25+ and/or the CD4+CD28-phenotype in long-term BOS- LT patients. We will determine their ability to suppress donor antigen-specific proliferation and IL-2 production and the mechanism of inhibition. And 4) To define the role of innate immunity, in particular TOLL receptors, in the pathogenesis of BOS. Specifically, we will determine the expression levels of SIGIRR in lung tissues, TLR expression, activation of NF-kappaB, production of chemokines and pro-inflammatory cytokines and correlate the results with the development of BOS. The overall goal of this application is to define the cellular and molecular mechanisms involved in the pathogenesis of BOS subsequent to LT in order to institute new therapeutic strategies that will prevent the development of this disease.